During recent years attempts have been made to utilize "total station" electronic instrumentation in high order surveying to provide computer-processible data relating to the distance and difference in elevation between measuring stations, or between a measuring station and a previously established benchmark. While electronic distance measuring (EDM) components of such instrumentation have been developed to a degree such that the line-of-sight, or slant, distance between stations can readily be determined in a short time with high order accuracy, elevation measurement continues to require substantial preparation time and extended periods of manipulation to obtain high order data.
A basic problem with presently available electronic elevation measuring instrumentation lies in its continued reliance upon elevation angle determination in the manner of the surveying theodolite of which it is normally a part. In such practice, as is described, for example, in U.S. Pat. No. 4,146,927, measurement usually entails establishing the horizontal datum plane of the line of sight of the instrument, displacing this line of sight by pivoting the entire telescope or sighting element about the horizontal axis of the alidade sufficiently to acquire the target, determining the angular degree of such pivoted displacement from the datum, and applying the measured degree of such pivoting and the measured distance between the station and the target to determine trigonometrically the difference in elevation. The fact that high order surveying requires resolution of the extent of such pivoted angular displacement to within 0.5 arc second readily indicates the essence of the problem encountered with instrumentation available to the surveyor prior to the present invention.
An additional concern in modern high order surveying is the need for a system which will provide volume productivity through mobility and rugged construction, yet will retain the accuracies normally associated only with more fragile and delicate instrumentation. Such a practical system must also enable short elapsed station time by allowing rapid set-up, stabilization, and measurement data acquisition. The instrument and measuring procedure of the present invention effectively satisfy these various requirements, and provide today's mechanized surveyor with the means for accomplishing wide range high order network surveying with minimum delay and difficulty.